What do your friends see on Facebook when they look for your email address? It might not be what you think. In the past few days, Facebook automatically changed the email contacts it displays without clearly notifying users about what it was doing.

As NPR's Laura Sydell reports, lots of people on Facebook are not happy.

LAURA SYDELL, BYLINE: Among the first to notice the change was blogger Gervase Markham, an occasional Facebook user. He saw that his contact was suddenly listed as his name at Facebook.com. He was annoyed.

GERVASE MARKHAM: What they had effectively done is replaced my displayed form of contact information with contact information that pointed, it turns out, back to their site into an inbox that I never look at.

SYDELL: In other words, instead of having emails sent directly to him, he would have to check his Facebook message center to find his emails. It is possible to change it back but it isn't easy - I tried. You have to go to your personal Timeline, click on About, then go to the Contact Info, hit Edit - well, you get the point, it's a lot of steps.

Facebook created its own email feature back in 2010, but it hasn't really caught on.

MARKHAM: If Facebook wants to provide an email service, then they should provide it in a way that is compelling and that people want to use it, rather than that people are strongly nudged into using it by this kind of mechanism.

SYDELL: Facebook wouldn't talk to NPR about the change but it points to a statement it released back in April. The company said it did let users know this change was coming at the time it announced that it would be making updates to addresses on the site to make them consistent, though it didn't say anything about which email contact it would use. But Facebook has a history of making changes with inadequate notice.

Nate Elliott, an analyst at Forrester Research, says it's often ticked users off, especially when the company made unannounced changes to privacy settings. However, Elliott says, they've also had success in making changes without notice.

NATE ELLIOTT: And the first time anyone ever saw a newsfeed on Facebook, they said this is horrible - why would we want a newsfeed. Today, of course, the newsfeed is the very core of Facebook. And so, you know, if I'm at Facebook, I'm thinking our users don't necessarily know what they want.

SYDELL: Elliott says one of the major motivations for Facebook is staying relevant. Its executives are well-aware of the fate of doomed social networks like MySpace and Friendster.

ELLIOTT: It's not enough to simply offer the same services, the same features over an extended period of time to users. You need to constantly evolve a service to keep it interesting. And Facebook has been very good at doing this over the past several years.

SYDELL: Elliott says Facebook also want its users to stay on the site longer so it can show them more ads; important now that it's a public company with shareholders to keep happy.

User Gervase Markham isn't going to leave over the latest mishap. Analyst Elliott thinks that the vast majority of the social network's more than 900 million users will stick around even if they are a bit annoyed.